Agricultural vehicles are used under a wide range of operating conditions. The vehicles are used outdoors and may be required to traverse a paved road to move from a storage facility to a field and then traverse an unpaved surface getting to and working in the field. Some agricultural vehicles are driven using hydraulic motors. A separate hydraulic motor may be used on each wheel. A hydraulic pump may be located on the vehicle to generate hydrostatic pressure. A hydraulic line connects the hydraulic pump to each hydraulic motor. The amount of hydrostatic pressure generated by the hydraulic pump determines the amount of torque applied to each wheel by the hydraulic motor.
Historically, the hydraulic systems include a user interface, such as a joystick, to receive a speed command from the operator. For example, the operator may push the joystick either forward or reverse to command forward or reverse operation of the agricultural vehicle. The amount of deflection of the joystick from a neutral position corresponds to the speed at which the operator wishes to travel.
Agricultural vehicles are further equipped with service brakes to slow and stop the vehicle. The service brakes use conventional braking components such as brake pads applied to a brake rotor or brake shoes applied to a brake drum. A brake pedal may be pressed by the operator to activate the service brakes.
Under emergent or quick stopping conditions, however, the potential exists for the operator to be commanding motion of the agricultural vehicle via the joystick and be required to quickly activate the service brakes. Under these conditions, the hydraulic system may be driving through the service brakes, causing excessive wear and/or premature failure of the service brakes.
Thus, it would be desirable to provide an improved braking system for an agricultural vehicle propelled by a hydrostatic drive unit.